CAREER: Investigating Strong Electron-Phonon Interactions in Semiconducting Crystals Using Reciprocal-Space Quantum-Classical Modeling

在化学系化学理论、模型和计算方法(CTMC)计划的支持下，西北大学的Roel Tempelaar将研究用于光电子器件和信息技术的半导体材料中电子和核振动(声子)之间的强相互作用。各种变革性材料的电子-声子耦合强度超过了常用半导体的强度，实现了全新的功能，但也促使人们需要将准确性与可扩展性相结合的新的预测理论方法。Tempelaar和他的团队旨在通过开发用量子力学描述电子而用经典描述原子核的方法来解决这一需求。通过采用相关坐标的动量表示法，可以模拟超大尺寸的材料。这开启了定量理解和控制材料行为的途径，对高效收集太阳能和将量子态用于节能和安全的信息技术具有重要意义。这项研究与解决附近经济困难的高中生中的代码文盲问题的教育部分相结合。这一组成部分旨在通过基于丰富的智能手机技术构建一系列引人入胜的编码练习，在课堂环境之外培养编码暴露。在各种新兴的晶体半导体类别中，包括金属卤化物钙钛矿和过渡金属二卤化物，电子-声子耦合比无机材料的典型情况更强。虽然这种耦合强度产生了独特的光物理性质，但它们提出了非微扰建模的需要，以便解开它们的机械原理。Tempelaar和他的团队试图通过重新制定量子经典动力学方法来解决这一需求，这些方法通常用于描述晶体激发的Bloch态。在Bloch表示中，可以执行基截断，这将显著降低模拟成本。这将使该团队能够解决光激发的演变，手征声子模式产生的光物理，以及现实条件下六角晶格中耦合自旋-动量态的动力学。通过这项研究计划，Tempelaar团队中的研究生和博士后研究人员将接触到理论化学、物理和材料科学的技术组合，促进他们作为跨学科科学家的发展。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Chemical Theory, Models and Computational Methods (CTMC) program in the Division of Chemistry, Roel Tempelaar of Northwestern University will study strong interactions between electrons and nuclear vibrations (phonons) in semiconducting materials for use in optoelectronic devices and information technologies. Various transformative materials feature electron-phonon coupling strengths exceeding those seen for commonly-used semiconductors, enabling radically new functionalities, but also prompting the need for new predictive theoretical methodologies that combine accuracy with scalability. Tempelaar and his team aim to address this need by developing methods where electrons are described quantum-mechanically while nuclei are described classically. By adopting a momentum representation of the involved coordinates, materials of exceedingly large sizes can be simulated. This opens ways to quantitatively understand and control material behaviors, with implications for the efficient harvesting of solar energy and the use of quantum states for energy-efficient and secure information technologies. This research is integrated with an educational component addressing code illiteracy among economically-disadvantaged nearby highschoolers. This component aims to foster coding exposure beyond a classroom environment by constructing an engaging sequence of coding exercises based on abundant smartphone technology.In various emerging classes of crystalline semiconductors, including metal-halide perovskites and transition-metal dichalcogenides, electron-phonon couplings are stronger than typically found for inorganic materials. While such couplings strengths give rise to unique photophysical properties, they pose the need for non-perturbative modeling in order to unravel their mechanistic principles. Tempelaar and his team seek to address this need by reformulating quantum-classical dynamical methods in terms of Bloch states commonly used to describe crystal excitations. Within the Bloch representation, basis truncations can be performed that will significantly reduce the cost of simulations. This should enable the team to address the evolution of photo-excitations, the photophysics emerging from chiral phonon modes, and the dynamics of coupled spin-momentum states in hexagonal lattices under realistic conditions. Through this research program, graduate students and postdoctoral researchers in the Tempelaar team will be exposed to a combination of techniques from theoretical chemistry, physics, and materials science, fostering their development as cross-disciplinary scientists.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.